This invention relates to a fluorescent screen structure and a field emission display (FED) and methods for manufacturing these, and for example relates to a color fluorescent screen structure for various types of display and a field emission display using this fluorescent screen structure having field emission cathodes as electron sources and to methods for manufacturing this color fluorescent screen structure and display.
Generally, as methods for making fluorescent screens in color cathode ray tubes (including monochrome tubes), slurry methods, printing methods or electrodeposition have been used.
However, with a fluorescent screen panel for an FED, many column-shaped bodies several hundreds of .mu.m tall called pillars which withstand the high vacuum inside the panel and support the vacuum are formed before the fluorescent substances are applied, and it is necessary to coat the fluorescent substances in the gaps between these numerous pillars.
Because of this, with the slurry methods and printing methods that have been used conventionally, the pillars constitute solid obstructions in the process and it has been difficult to form an even fluorescent screen. Furthermore, because an organic material has been used as the bonding material, it has not been possible to completely remove this material just by burning it off in a baking step. For example, when forming a color fluorescent screen in an FED it is necessary to maintain an ultra-high vacuum of about 10.sup.-8 Torr inside the display, but with slurry methods there has been the problem that gas emitted by the fluorescent screen as a result of the presence of the organic material mentioned above causes the vacuum to deteriorate.
With the electrodeposition method it is possible to coat a fluorescent substance onto predetermined areas (areas of an electrode pattern) irrespective of the existence of the pillars, and because there is no gas emission from the coated film it is also possible to maintain a high vacuum. The present inventors have already proposed forming a fluorescent screen for an FED by making the best use of the advantages of the electrodeposition method (Japanese Patent Applications Nos. H.4-225994, H.6-76738). According to a method disclosed in these previous applications, when electrodepositing a fluorescent substance of a certain color on selected electrodes, by applying a zero or reverse polarity voltage (reverse bias) on non-selected electrodes on which the fluorescent substance is not to be electrodeposited, unwanted adhesion of the fluorescent substance to the non-selected electrodes can be prevented.
With this electrodeposition method, a fluorescent substance to be deposited is dispersed in a water-soluble or non-water-soluble electrodeposition solution containing an electrolyte (added to positively or negatively charge the fluorescent substance); bodies to be electrodeposited on (electrodes on the inner side of a panel) and an opposing electrode are disposed facing each other in the electrodeposition solution with an inter-electrode distance normally of the order of several tens of mm provided therebetween, and a fluorescent screen is formed by electrodepositing the fluorescent substance onto the electrodes with the electrode side being given a negative potential and the opposing electrode side being given a positive potential when the fluorescent substance is charged positively and the electrode side being given a positive potential and the opposing electrode side being given a negative potential when the fluorescent substance is charged negatively.
For example, as proposed in Japanese Patent Publication No. S.60-11415, to form a color fluorescent screen consisting of fluorescent substances of the colors green, blue and red, fluorescent substances of these three colors are electrodeposited one after another on stripelike transparent electrodes by repeating the above process for each of the colors.
However, the present inventors have discovered as a result of studies into techniques for coating a fluorescent substance onto a fluorescent screen panel by this electrodeposition method that there are the following problems to be solved:
First, for such reasons as that conventionally electrodeposition has been carried out with the opposing electrode (facing electrode) only disposed parallel to the fluorescent screen panel surface with a predetermined distance (for example of the order of 40 to 50 mm) therebetween and that during electrodeposition the charged fluorescent substance particles actually involved in electrodeposition brought about by electrophoresis are only those within a small distance from the surface being electrodeposited on (this distance varies with the electrodeposition time but at the most is about 1 mm), the fine control of the field strength applied to the charged fluorescent substance particles necessary to achieve an electrodeposition coating on a narrow stripe pattern with good precision is difficult and as a result it has not always been possible to realize the even formation of a very fine fluorescent screen.
Also, in electrodeposition onto electrodes of narrow stripe pattern, the spaces between the stripes also naturally are narrow, and with conventional electrodeposition methods there has been the problem that electrodeposition is also carried out on spaces around the stripe electrodes to be electrodeposited on and on adjacent stripe electrodes, and mixed colors tends to occur.
There has also been the problem that because the opposing electrode is disposed a fixed distance from the fluorescent screen panel surface the electrodeposition tank itself is large, a large quantity of solution is used and consequently it is difficult to uniformly stir and circulate the electrodeposition solution.